Modern integrated circuits (ICs) and electronic assemblies, and the devices therein, are at risk of damage due to electrostatic discharge (ESD) events. Accordingly, it is commonplace to provide an ESD protection clamp across the terminals of such devices, IC's and electronic circuits or assemblies. As used herein, the term integrated circuit and the abbreviation IC are intended to refer to any type of circuit or electronic assembly whether formed in a monolithic substrate or as individual elements or a combination thereof.
ESD protection clamps are circuit elements used to protect IC devices from voltage and current spikes that may be associated with an electrostatic discharge. To protect an IC device, an ESD clamp is connected between an input or output terminal of the IC device and a ground or common terminal. During normal operation, the ESD clamp does not conduct. But when subjected to an excessive voltage, the ESD clamp becomes conductive, conducting current to ground and limiting voltage across the IC device to a desired safe level, thereby protecting the IC to which the ESD clamp is connected. Generally, the ESD will turn on or become conductive at a voltage that is above the DC operating voltage of IC device, but below the IC device's breakdown voltage.